In many applications requiring structural members such as studs, beams, decking, framing members, trim pieces, and railings, polymeric materials have replaced wood. Window frames and shutters are made of hollow vinyl profiles. Interior molding and, more recently, screen doors, are made of foamed polyvinyl chloride.
Plastics have advantages over wood, including lower cost and lower maintenance, but often do not have the inherent strength of wood without incorporating other materials, such as wood or metal inserts, as secondary reinforcements to increase stiffness. Adding these types of secondary reinforcements increases the cost of material and labor and introduces complexity because of the additional type of material required.
Structural composites are well known. For example, U.S. Pat. No. 4,910,067, discloses a structural composite material comprising a foam core with a thermoplastic layer on one side and a layer of fibrous material on the other. The foam is formed from a liquid resin, which cures in contact with the fibrous material, impregnating and bonding it into a fiber-reinforced structure. A process for manufacturing the composite is taught in this prior art reference.
U.S. Pat. No. 5,700,555 teaches a composite article comprising a first zone made entirely of plastic and a second zone made of plastic plus 10% to 55% natural fiber, both of which are formed by co-extrusion. The fiber-containing zone includes embossing to resemble wood grain and is sufficiently porous to accept paint or stain to simulate the appearance of natural wood.
U.S. Pat. Nos. 5,738,935 and 5,858,522, are related to each other and to U.S. Pat. No. 5,700,555, described above, and disclose a process for the preparation of a natural fiber and thermoplastic composite and the resulting products therefrom. The process includes the steps of mixing the synthetic fiber and the thermoplastic in a blender with a porosity aid and an interfacial agent to form a mixture; adding the mixture to a heated extruder; extruding the mixture as a composite; and shaping the composite in a vacuum calibration device to a desired profile. The process further includes the step of co-extruding a second thermoplastic onto the natural fiber/thermoplastic composite for some applications (e.g., windows, doors and siding).
EP 0599404 discloses a process for preparing thermoplastic composites reinforced with continuous fibers. The process includes the steps of: (a) unwinding a continuous filament, constituted by a bundle of fibers, from a bobbin; (b) opening the continuous filament, essentially by disassembling it into its individual continuous fibers; (c) dipping and driving the open filament through a stationary bed consisting of a thermoplastic polymer powder contained in a tank that is submitted to continuous vibration; and (d) reassembling the filament and arranging around it a sheltering flexible sheath made of a thermoplastic polymer.
EP 0653290, discloses a continuous process for producing a molded thermoplastic fiber-reinforced article having a high resin concentration in at least one surface by coating the surface of that heated fiber mat core with a melted first thermoplastic resin, and then passing the fiber mat core into an extrusion zone wherein a melted second thermoplastic resin is extruded onto it. Then the fiber mat core and thermoplastic resin are molded into a finished article. The continuous process disclosed provides molded finished articles such as roof tile, automobile exterior panels, house siding, etc.
U.S. Pat. No. 5,565,056 discloses a glass fiber-reinforced building panel made by extruding molten first and second webs of polymer compounds through spaced die openings, positioning a mat of randomly oriented short glass fibers between the first and second webs, pressing the webs and mat together, and cooling the resulting building panel.
EP 0747213 discloses a panel comprising a first layer of polypropylene filled with sawdust, wood flour, or wood shavings and at least one additional layer consisting at least partially of fibrous thermoplastic material that are bonded to one face of the first layer by compression and simultaneous, partial fusion. This additional layer retains the fibrous pattern and structure.
U.S. Pat. No. 6,607,798 discloses a fiber-reinforced, hollow-center, composite hollow structure in which hollow center cores made of thermoplastic resin are joined into one body by intermediate layers containing reinforcing long fibers bonded to each other with a thermosetting resin. The structure is then covered with an outer layer of thermoplastic resin.
U.S. Pat. No. 9,079,380 discloses co-extrusion of polyvinyl chloride (PVC) with a composite material, forming a continuous strip which may then be cut into convenient lengths. The PVC forms mounting flanges and ventilation standoffs on the back surface only, with all parts on the front being formed of a composite of cellulose fiber and a thermoplastic resin.
A polymeric composition that has structural levels of stiffness and low manufacturing cost would be advantageous particularly if it conserved natural resources by recycling previously-used materials.